Many conventional drilling rigs use a top-drive for pulling pipe and/or tools from a well bore. Powerful motors are used to pull and wind wire rope, cable or strand about a drum located above the derrick floor. Swivels are used in-line with helical wound members such as rope, cable or strand for allowing rotation about a longitudinal axis thereof under tension for minimizing or avoiding straightening of the helical windings in order to protect the strength and integrity of the rope, cable or strand by compensating for the torsional force induced by large axial forces on the helical member. Typical forces can be on the order of several tons, or more.
In one typical operation referred to as a “wireline strip over operation”, a sinker bar is used in-line with the wire rope. Sinker bars have in the past been comprised of a rigid member which may be in the form of a solid bar on the order of 15 to 20 feet in length. Use of such a sinker bar with a top drive creates interference between the sinker bar and rig equipment located vertically above the drill pipe; heretofore, it has been necessary to move and relocate the top drive unit out of the way. This is a time consuming operation that is best to be avoided.